• Earthquakes and Structures
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• v.5 no.2
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• pp.129-142
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• 2013

Linear and nonlinear time history analyses have been becoming more common in seismic analysis and design of structures with advances in computer technology and earthquake engineering. One of the most important issues for such analyses is the selection of appropriate acceleration time histories and matching these histories to a code design acceleration spectrum. In literature, there are three sources of acceleration time histories: artificial records, synthetic records obtained from seismological models and accelerograms recorded in real earthquakes. Because of the increase of the number of strong ground motion database, using and scaling real earthquake records for seismic analysis has been becoming one of the most popular research issues in earthquake engineering. In general, two methods are used for scaling actual earthquake records: scaling in time domain and frequency domain. The objective of this study is twofold: the first is to discuss and summarize basic methodologies and criteria for selecting and scaling ground motion time histories. The second is to analyze scaling results of time domain method according to ASCE 7-05 and Eurocode 8 (1998-1:2004) criteria. Differences between time domain method and frequency domain method are mentioned briefly. The time domain scaling procedure is utilized to scale the available real records obtained from near fault motions and far fault motions to match the proposed elastic design acceleration spectrum given in the Eurocode 8. Why the time domain method is preferred in this study is stated. The best fitted ground motion time histories are selected and these histories are analyzed according to Eurocode 8 (1998-1:2004) and ASCE 7-05 criteria. Also, characteristics of both near fault ground motions and far fault ground motions are presented by the help of figures. Hence, we can compare the effects of near fault ground motions on structures with far fault ground motions' effects.

• Structural Engineering and Mechanics
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• v.55 no.5
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• pp.1055-1086
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• 2015

The dynamic response of two-dimensional unbounded domain on the rigid bedrock in the time domain is numerically obtained. It is realized by the modified scaled boundary finite element method (SBFEM) in which the original scaling center is replaced by a scaling line. The formulation bases on expanding dynamic stiffness by using the continued fraction approach. The solution converges rapidly over the whole time range along with the order of the continued fraction increases. In addition, the method is suitable for large scale systems. The numerical method is employed which is a combination of the time domain SBFEM for far field and the finite element method used for near field. By using the continued fraction solution and introducing auxiliary variables, the equation of motion of unbounded domain is built. Applying the spectral shifting technique, the virtual modes of motion equation are eliminated. Standard procedure in structural dynamic is directly applicable for time domain problem. Since the coefficient matrixes of equation are banded and symmetric, the equation can be solved efficiently by using the direct time domain integration method. Numerical examples demonstrate the increased robustness, accuracy and superiority of the proposed method. The suitability of proposed method for time domain simulations of complex systems is also demonstrated.

• Earthquakes and Structures
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• v.6 no.4
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• pp.375-392
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• 2014

Time history analyses have been preferred commonly in earthquake engineering area to determine earthquake performances of structures in recent years. Advances in computer technology and structural analysis have led to common usage of time history analyses. Eurocode 8 allows the use of real earthquake records as an input for linear and nonlinear time history analyses of structures. However, real earthquake records with the desired characteristics sometimes may not be found, for example depending on soil classes, in this case artificial and synthetic earthquake records can be used for seismic analyses rather than real records. Selected earthquake records should be scaled to a code design spectrum to reduce record to record variability in structural responses of considered structures. So, scaling of earthquake records is one of the most important procedures of time history analyses. In this paper, four real earthquake records are scaled to Eurocode 8 design spectrums by using SESCAP (Selection and Scaling Program) based on time domain scaling method and developed by using MATLAB, GUI software, and then scaled and real earthquake records are used for linear time history analyses of a six-storied building. This building is modeled as spatial by SAP2000 software. The objectives of this study are to put basic procedures and criteria of selecting and scaling earthquake records in a nutshell, and to compare the effects of scaled earthquake records on structural response with the effects of real earthquake records on structural response in terms of record to record variability of structural response. Seismic analysis results of building show that record to record variability of structural response caused by scaled earthquake records are fewer than ones caused by real earthquake records.

• Journal of electromagnetic engineering and science
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• v.9 no.4
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• pp.211-217
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• 2009

A three-dimensional locally one-dimensional multiresolution time-domain(LOD-MRTD) method is introduced and unconditional stability is proved analytically. The updating formulations have fewer terms on the right-hand side than those of an alternating direction implicit MRTD(ADI-MRTD). The validation of the method is presented using the resonance frequency problem of an empty cavity. The reduction of the numerical dispersion technique is also combined with the proposed method. The numerical examples show that the combined method can improve the accuracy significantly.

• Journal of Mechanical Science and Technology
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• v.20 no.7
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• pp.950-960
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• 2006

An output time delay always exists in practical systems. Analysis of the delay phenomenon in a continuous-time domain is sophisticated. It is appropriate to obtain its corresponding discrete-time model for implementation via a digital computer. A new method for the discretization of nonlinear systems using Taylor series expansion and the zero-order hold assumption is proposed in this paper. This method is applied to the sampled-data representation of a nonlinear system with a constant output time-delay. In particular, the effect of the time-discretization method on key properties of nonlinear control systems, such as equilibrium properties and asymptotic stability, is examined. In addition, 'hybrid' discretization schemes resulting from a combination of the 'scaling and squaring' technique with the Taylor method are also proposed, especially under conditions of very low sampling rates. A performance of the proposed method is evaluated using two nonlinear systems with time-delay output.

• Journal of Mechanical Science and Technology
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• v.19 no.11
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• pp.1975-1987
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• 2005

An input time delay always exists in practical systems. Analysis of the delay phenomenon in a continuous-time domain is sophisticated. It is appropriate to obtain its corresponding discrete-time model for implementation via digital computers. In this paper a new scheme for the discretization of nonlinear systems using Taylor series expansion and the zero-order hold assumption is proposed. The mathematical structure of the new discretization method is analyzed. On the basis of this structure the sampled-data representation of nonlinear systems with time-delayed multi-input is presented. The delayed multi-input general equation has been derived. In particular, the effect of the time-discretization method on key properties of nonlinear control systems, such as equilibrium properties and asymptotic stability, is examined. Additionally, hybrid discretization schemes that result from a combination of the scaling and squaring technique (SST) with the Taylor series expansion are also proposed, especially under conditions of very low sampling rates. Practical issues associated with the selection of the method's parameters to meet CPU time and accuracy requirements, are examined as well. A performance of the proposed method is evaluated using a nonlinear system with time delay maneuvering an automobile.

• Journal of the Korea Society of Computer and Information
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• v.3 no.3
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• pp.99-106
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• 1998

This Paper proposes a novel fractal image method for image communication to shorten time to take on fractal encoding by using limited search area method and scaling method First, the original image is contracted respectively by half and by quarter with the scaling method. And then, the corresponding domain block of the quarter-sized image which is most similar with one range block of the half-sized image is searched within the limited area in order to reduce the encoding time extremely As the result of the evaluation, the proposed algorithm provided much shorter encoding time and better compression ratio with a little degradation of the decoded image quality than Jacquin's method.

• Interaction and multiscale mechanics
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• v.2 no.4
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• pp.353-374
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• 2009

A new seamless multiscale simulation was developed for coupling the continuum model with its molecular dynamics. Kriging-based Finite Element Method (K-FEM) is employed to model the continuum base of the entire domain, while the molecular dynamics (MD) is confined in a localized domain of interest. In the coupling zone, where the MD domain overlaps the continuum model, the overall Hamiltonian is postulated by contributions from the continuum and the molecular overlays, based on a quartic spline scaling parameter. The displacement compatibility in this coupling zone is then enforced by the Lagrange multiplier technique. A multiple-time-step velocity Verlet algorithm is adopted for its time integration. The validation of the present method is reported through numerical tests of one dimensional atomic lattice. The results reveal that at the continuum/MD interface, the commonly reported spurious waves in the literature are effectively eliminated in this study. In addition, the smoothness of the transition from MD to the continuum can be significantly improved by either increasing the size of the coupling zone or expanding the nodal domain of influence associated with K-FEM.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.438-440
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• 2004

Energy consumption has become an increasingly important consideration in designing real-time embedded systems. In this paper, we propose a voltage scaling method to reduce energy consumption in fixed priority real-time systems using variable voltage processors. The Hyperperiod of tasks is divided into dimains. The most suitable voltage of each domain is determined off-line and stored in a table. During task execution, the voltage of processor is adjusted according to the information of the table. A simulation result shows that the proposed method can reduce 80% of power consumption in comparison to no power management. The difference to the optimal EDF based method is only 5%.

• Journal of electromagnetic engineering and science
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• v.13 no.3
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• pp.158-164
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• 2013

This paper expands a previously proposed optimized higher order (2, 4) finite-difference time-domain scheme (H(2, 4) scheme) for use with lossy material. A low dispersion error is obtained by introducing a weighting factor and two scaling factors. The weighting factor creates isotropic dispersion, and the two scaling factors dramatically reduce the numerical dispersion error at an operating frequency. In addition, the results confirm that the proposed scheme performs better than the H(2, 4) scheme for wideband analysis. Lastly, the validity of the proposed scheme is verified by calculating a scattering problem of a lossy circular dielectric cylinder.